With the recent progress in base sequence analysis technology, all base sequences of the human genomes have been analyzed and diverse utilization of DNA base sequence information in the medical field has been developed actively. Now it is expected that individual body types will be analyzed as well as diseases diagnosed at the individual level by understanding the status of gene expression in the biological systems in an attempt to contribute to individualized medical care suited for individual body types. We expect a dramatic development in broad fields including genetic engineering for agricultural products besides the development in medicine. The basis of such development is information on gene expression and functional information as well as information on base sequences. Currently functions of genes are investigated in a large scale using DNA chips and the expressions are being analyzed. Since a fluorescent detection method is the basic principle when using DNA chips and laser beams and complicated optical systems are required, the measurement systems are large and cost more. In order to circumvent the above problems, current detection type DNA chips using redox labeled materials or DNA sensors by detecting surface potentials using electrical characteristics of transistors have been reported. For the DNA chips using electrical measurements, it is easier to develop smaller equipment and the manufacturing cost can be reduced easily. Therefore, DNA chips using electrical measurements are currently attracting tremendous attention as a method suited for large capacity.
A current detection method using redox labeled materials is based on the properties that redox materials undergo intercalation among the double stranded DNA formed by binding of a target DNA to a DNA probe (called hybridization). The presence/absence of bindings between the target DNA and the DNA probe (hybridization) is determined by detecting the reception of electrons between the intercalated redox materials and the metal electrodes (Analytical Chemistry 66, (1994) 3830-3833).
According to the surface potential detection method using the electrical characteristics of transistors, a DNA probe is immobilized on the gate insulating layer on the source electrode and drain electrode, and the surface potential on the insulating film (surface charge density) when the target DNA binds to the DNA probe (hybridization) is then detected as changes in the current values between the source electrode and the drain electrode (Published Japanese translation of PCT international publication for patent application No. 511245/2001). As a gate insulator, materials such as silicon oxide, silicon nitride, and tantalum oxide are combined or used alone. In order to maintain good operation of transistors, a double structure is prepared by laminating silicone nitride or tantalum oxide on silicon oxide. In order to immobilize the DNA probe on the gate insulating layer, the gate insulating material surface is chemically modified using aminopropyl silane or polylysine to introduce amino groups and the DNA probe that has been chemically modified by the terminal amino groups is reacted using glutaraldehyde and phenylenediisocyanate.    [Non-patent Document 1] Analytical Chemistry 66, (1994) 3830-3833    [Patent Document 1] Published Japanese translation of PCT international publication for patent application No. 511245/2001